1. Field of the Invention
This invention relates to a laser beam scanner and a photographic printer using the laser beam scanner as an exposure apparatus for exposing a photographic paper.
2. Description of the Related Art
A conventional a photographic printer using a laser beam scanner as an exposure apparatus, for example, shown in Publication Gazette of Japanese Patent application Hei 11-84293 is described. In the photographic printer, a photographic paper is conveyed in a predetermined direction (hereupon, the direction is called xe2x80x9csub-scanning directionxe2x80x9d) at a predetermined constant speed. Laser beams corresponding to three primary colors or complementary colors thereof are scanned on a photo-sensitive surface of the photographic paper in a main scanning direction perpendicular to the sub-scanning direction. Intensities of the laser beams are respectively modulated for corresponding to an image data which is taken by scanning a film or photograph by an image pickup scanner or directly taken by a digital camera, or the like.
When the scanning lines of the laser beams corresponding to the principal colors are discrepant, it will be the cause of reduction of quality of an image formed on the photographic paper, since bleeding occurs in color development. For preventing the occurrence of the bleeding of colors, optical paths of the laser beam scanner corresponding to the laser beams are precisely adjusted in a manner so that scanning lines of the laser beams are overlapped with each other on the photographic paper.
In an assembly of a unit of laser beam scanner provided in the conventional photographic printer, a measuring instrument is disposed at a predetermined position on an optical table optically conjugated with a predetermined scanning plane of a conveyor for conveying the photographic paper. The optical paths of the laser beams are adjusted to be overlapped on the measuring instrument while the laser beams have been irradiated. Alternatively, a previously assembled unit of the laser beam scanner is mounted in the photographic printer, and the measuring instrument is directly disposed at a predetermined position on the scanning plane of the conveyor, and the optical paths of the laser beams are adjusted. It, however, requires much labor to adjust the optical path, for example, by adjusting a reflection angel of a mirror with monitoring the laser beams scanning on the measuring instrument and to dispose the measuring instrument at the predetermined position on the optical table at or on the conveyor in the photographic printer precisely.
Furthermore, it is necessary to interchange electronic elements such as a laser light source and an optical modulator, since the electronic elements have a shorter-life than that of optical elements such as a mirror and a lens. When at least one element is interchanged, it is necessary to re-adjust the optical paths of the laser beams. It, however, is substantially impossible to re-adjust the optical paths of the laser beams, since other elements of the photographic printer occupy the space into which the above-mentioned measuring instrument is disposed on the conveyor, after the completion of the assembly of the photographic printer. Thus, whole unit of the laser beam scanner is generally interchanged after the completion of the photographic printer.
An object of the present invention is to provide a laser beam scanner and a photographic printer using the same, by which optical paths of the laser beams can be adjusted without using the measuring instrument disposed on a scanning line on which the laser beams be scanned.
A laser beam scanner in accordance with the present invention comprises at least two laser light sources for oscillating and emitting at least two leaser beams having different wavelength, an optical scanning system for scanning the laser beams on a predetermined scanning plane, and an optical paths adjusting system for adjusting optical paths of the optical scanning system. The optical paths adjusting system includes a position sensor disposed on a plane optically conjugated with the predetermined scanning plane, and at least an adjuster for adjusting an optical path of a laser beam corresponding to the adjuster.
By such a configuration, since the position sensor is disposed on the plane optically conjugated with the scanning plane, the positions where the laser beams reach on the position sensor correspond to the positions on the scanning plane where the laser beams actually will be scanned. When the positions of the laser beams on the position sensor are not coincided, it is possible to adjust the adjuster so that at least one position of the laser beam coincides with or approaches to another position of the laser beam by monitoring the sensed result of the position sensor. As a result, at least two optical paths of the laser beams can be adjusted so as to overlap the scanning lines of the laser beams with each other.
A photographic printer in accordance with the present invention includes the above-mentioned laser beam scanner, a conveyor for conveying a photographic paper to the predetermined scanning plane of the above-mentioned laser beam scanner and a developer for developing a latent image exposed on the photographic paper by the laser beam scanner.
By using the above-mentioned laser beam scanner as an exposure unit, the optical paths of the scanning system in the laser beam scanner can be adjusted easily without disassembly of the photographic printer largely, when the electronic element such as the laser light source is interchanged due to the deterioration thereof.